Recycling of non-biodegradable solid wastes is an urgent problem in a world that increasingly is polluted with man-made materials. “Recycling” by definition is any process in which waste products or materials are recovered, cleaned up and reconditioned, and ultimately reused. “Upcycling” relates to processes by which recovered waste materials are transformed into products of greater value. Of the 300 million tons of solid trash generated by Americans annually only 30% is recycled or composted. Of the total waste, about 60% is biodegradable, including 15% food, 14% yard trimmings, 27% paper, and 6% wood. Of the non-biodegradable materials, the major fraction of solid waste ends up in landfills after a single use cycle. Very little material is actually recovered and almost none is converted to products of greater value.
At this time, only a very small amount of material is recovered by manufacture into new products. Waste rubber (mostly as discarded tires), roofing materials (mostly as bituminous shingles in mixed construction trash), and synthetic fibers (mostly as waste carpet) are representative of waste materials that are essentially impossible or extremely expensive and difficult to market. These materials are not compostable and, even buried, remain in the environment for centuries. For years these three waste streams were not in demand because it was much cheaper to dispose of the material in a landfill. But with landfills closing due to high costs of permitting and operating, the costs of disposal are now increasing to the point that throwing a product or material away is more expensive than recovering it for re-use in new ways.
Tires have been the subject of attempts to recycle the material. The process of chipping waste tires is well known and results in a free-flowing “crumb rubber” material consisting of #10-#13 mesh rubber particles. Other grades up to pellet size are also available. Crumb rubber has been used to make synthetic turf, playground flooring, welcome mats, vehicle mudguards, or may be used as a liner or a cover for landfills. Despite these uses, a large fraction of waste tires end up buried in landfills, are disposed of illegally in rivers and streams, or are incinerated. Vulcanized rubber cannot be remelted and burns with a thick acrid smoke that reduces air quality.
Of equal concern, private interests have cleared vast sections of rainforest in Vietnam, Cambodia and Myanmar for rubber plantations, replacing vibrant ecosystems with monoculture that destroys the soil and causes downstream flooding. The land grab, fueled by futures trading, is built on a product that is used once and thrown away. About 1 billion “end-of-life” tires are discarded globally each year (approximately 20 million tons). About half of this “end-of-life” tire waste is ultimately burned and releases harmful emissions. According to Wikipedia, at least 14% of used tires are buried in landfills. Many are thrown illegally into rivers, lagoons or any land that is not aggressively policed.
Carpet disposal is on the order of 2-3 million tons a year in the USA and 4-6 million tons annually worldwide. Carpet waste may be, to some extent, recovered as a plastic resin and used to create new products such as recycled carpet, fibers, park benches, auto parts, parking stops, and backing layers, for example. Complete recovery of the resin relies on solvent-assisted depolymerization into component monomers such as the caprolactam units of nylon. Melt blending of thermoplastic fibers is another option, but while producing valuable new products, the remelt is an expensive process heavily dependent on careful sorting and washing of waste carpet by chemical type. Alternatively, carpet waste may be incinerated, the emissions contributing to poor air quality. Perhaps most harmful, carpet waste is often not separated for recovery and is disposed of in landfills. The fibers are not always biodegradable and may leach chemicals or microfiber particulates into water for hundreds of years.
Most bituminous roofing shingle scrap waste is disposed of by landfilling. The shingle sheets (termed in the industry “3-tab”) lack strength and are impossible to handle and recycle without further breakage. Most of the waste contains roofing nails. The grit applied to the exterior surface of the material limits scrap recovery for high-value products. Only a small amount of bituminous roofing shingles is recovered by admixture into asphalt paving; which can contain up to 3 to 4% (v/v) of shingle-derived waste.
As a general practice, recyclers first segregate materials by type and attempt to recycle the material for its original use. Plastics, for example, must be sorted before recycling is feasible. It would be desirable to add value by converting waste materials into products having properties superior to the waste of which the products are composed. Very little or no work has been done on conversion of solid waste streams by transformative processes that result in new products. Unlike biological waste that can be converted, for example, to liquid fuels, synthetic solid waste is generally regarded as a useless material, merely a problem for disposal, and is largely buried in landfills at great expense. However, disposal is not free, and is paid for by society, by the waste generator, or by future generations.
Thus, there is a need in the art for scalable waste stream recovery processes that can convert combinations of tire, roofing and fiber waste into new products with surprising strength, wear resistance, weatherability, and environmentally acceptable uses. Preferably, the products of the processes themselves are recyclable or may be recovered by adapting the same waste stream recovery process for multigenerational product manufacture.